In a gas turbine engine, operational efficiency generally increases as the temperature of the combustion stream increases. Higher combustion stream temperatures, however, may produce higher levels of nitrogen oxide (“NOx”) and other types of emissions that may be subject to both federal and state regulation in the United States and also subject to similar regulations abroad. A balancing act thus exists between operating the gas turbine engine in an efficient temperature range while also ensuring that the output of NOx and other types of regulated emissions remain below the mandated levels.
Several types of known gas turbine engine designs, such as those using Dry Low NOx (“DLN”) combustors, generally premix the fuel flows and the air flows upstream of a reaction or a combustion zone so as to reduce NOx emissions via a number of premixing fuel nozzles. Such premixing tends to reduce overall combustion temperatures and, hence, NOx emissions and the like.
Premixing, however, may present several operational issues such as flame holding, flashback, auto-ignition, and the like. These issues may be a particular concern with the use of highly reactive fuels. For example, it is possible for a flame to sustain in the head-end upstream of the fuel nozzles with any significant fraction of hydrogen or other types of fuels. Any type of fuel rich pocket thus may sustain a flame and cause damage to the combustor. Other premixing issues may be due to irregularities in the fuel flows and the air flows.
There is thus a desire for an improved combustor design. Such a combustor design should promote improved fuel-air premixing, particularly with the use of highly reactive fuels. Such combustors designs should promote such good mixing while maintaining emissions below mandated levels and avoiding or limiting issues such as flame holding, flashback, auto-ignition, and the like